Latching valves for controlling the flow of a liquid such as water are known. Typically in such a latching valve a solenoid is used to open and close the valve, and mechanical or magnetic means are used to latch the valve in open and closed positions. The solenoid, comprising a cylindrical plunger and a surrounding coil, is energized by introducing an electrical current in the coil to establish a magnetic field along the longitudinal axis of the plunger. The direction of the field depends upon the direction of current flow through the coil.
The plunger, under the influence of the axial magnetic field, moves in a direction along the lines of flux of the magnetic field. The direction of the lines of flux changes with the direction of the current through the coil. Accordingly, by reversing the polarity of the voltage applied to the ends of the coil, the direction of current through the coil, and thus the direction of the lines of flux and the movement of the plunger, may be reversed. Typically, one end of the plunger seats against a valve opening to provide a valve closed position, and moves away from the valve opening to provide a valve open position.
Latching means are provided to latch the position of the valve in either the open or closed positions. For example, a permanent magnet may be used to latch the valve in the open position while a spring may be used to latch the valve in the closed position. The magnet and the spring urge the plunger in opposite axial directions. An example of such a latching coil valve is shown in U.S. Pat. No. 5,584,465 to Ochsenreiter.
In Ochsenreiter, the closed position of the valve is changed to open by momentarily energizing the coil to create an axial magnetic force, in the direction opposite the spring force, which exceeds the spring force to move the plunger toward the permanent magnet. After the plunger moves to within close proximity of the permanent magnet, the coil may be deenergized because the force of the permanent magnet attracts the plunger to latch the valve in the open position. Conversely, the open position of the valve is changed to closed by momentarily energizing the coil to create an axial magnetic force, in the direction opposite the permanent magnet force, which reduces the permanent magnet force sufficiently to move the plunger in the same direction as the spring force. After the plunger has been moved a sufficient distance from the permanent magnet, the coil may be deenergized because the force of the spring urges the plunger to latch the valve in the closed position. Thus, the magnetic force provided by the coil is used only to bias the forces of either the magnet or the spring, in the open and closed valve positions, respectively, so that the other of the magnet or the spring may latch the valve in the appropriate position.
The Ochsenreiter latching coil valve, however, suffers from at least two identifiable drawbacks. First, in order to assure that the valve may operate consistently during valve opening and closing operations, the coil must be provided with a sufficient amount of current to assure that the developed axial magnetic force is always sufficient to overcome the force of the permanent magnet which latches the valve in the open position (to close the valve), or the force of the spring which latches the valve in the closed position (to open the valve). However, it is difficult to determine the precise amount of force required to be developed due to variances in the force of the permanent magnet and of the spring, and variances in coil constructions. Accordingly, a voltage must be applied across the coil leads sufficient to develop a magnetic force which is greater than that of either the spring or the permanent magnet.
In addition, the Ochsenreiter valve, being a direct acting valve, is not suitable for high flow applications of, for example, greater than one gallon per minute. Pilot operated valves for use in applications of several gallons per minute are known, as shown in U.S. Pat. No. 5,538,026 to Kazi. Pilot valves such as Kazi typically include a pilot valve member and a main valve member. To open the valve, the pilot valve member moves into the open position and the hydraulic force of the fluid forces the main valve member open. With the main valve member open, greater fluid flow from the inlet to the outlet is obtainable than would otherwise be attained if only the pilot valve member communicated between the inlet and the outlet. Kazi, however, does not provide means for latching the valve in the open and closed positions.
Accordingly, it is an object of the present invention to provide a pilot operated valve which can be latched in both the open and closed positions.
It is a further object of the present invention to provide a latching coil valve having means for latching which are adjustable so that the valve may be efficiently operated despite manufacturing variances in the latching means and the coil.